Jiuxiang Dai

The flexible lead halide perovskite@3-amino­propyl-triethoxysilane@bridged polysilsesquioxane (CsPbBr₃@APTES@BPSQ) luminescent films synthesis by simple and safe room temperature preparation. The CsPbBr₃@APTES@ BPSQ film showcases bright narrow-band photoluminescence and excellent environmental stability. The resulting films have broad potential for light-emitting diodes, high resolution PL imaging, and waterproof inks for information encryption and anti-counterfeiting applications.

Abstract

The inherent flexibility and excellent mechanical strength of lead halide perovskite quantum dots (LHP-QDs) films have attracted much attention in the fields of flexible lighting, displays, non-planar x-ray imaging, and wearable optoelectronics. Unfortunately, the complicated synthesis process and poor stability limit its practical applications, hence there is an urgent need to develop a feasible fabrication process for films to attain high device performance. Herein, a molecular level hybridization of bridged polysilsesquioxane (BPSQ) is designed as matrix to harvest both flexibility of organics and stability of inorganics, resulting in improved interfacial compatibility between the CsPbBr₃ QDs and the matrix through chemical bond anchoring. The CsPbBr₃@3-aminopropyl-triethoxysilane (APTES)@BPSQ films showcase bright narrow-band photoluminescence, with a photoluminescence quantum yield of 61% and a half-peak full width at half maximum of <17 nm. Notably, these films demonstrate excellent environmental stability, UV resistance, water stability (experiencing only an 18% decrease in luminescence intensity after 168 h of water immersion), and high-temperature stability (withstanding temperatures up to 500 K). Furthermore, white light-emitting diodes (WLEDs) and anti-counterfeiting patterns have been fabricated using CsPbBr₃@APTES@BPSQ, highlighting their wide application potential in flexible light-emitting devices and information encryption.

A space-confined chemical vapor deposition method is used to create ultrathin germanium telluride (GeTe) nanosheets, and the GeTe resonant bonding epitaxy results in thickness-dependent photoelectric properties. The ultrathin GeTe-based field-effect transistor exhibits excellent p-type behavior with an on/off ratio of 10⁵ and broad photodetection from 450–980 nm with a responsivity of 10³ A W^–1.

Abstract

As p-type phase-change degenerate semiconductors, crystalline and amorphous germanium telluride (GeTe) exhibit metallic and semiconducting properties, respectively. However, the massive structural defects and strong interface scattering in amorphous GeTe films significantly reduce their performance. In this work, two-dimensional (2D) p-type GeTe nanosheets are synthesized via a specially designed space-confined chemical vapor deposition (CVD) method, with the thickness of the GeTe nanosheets reduced to 1.9 nm. The space-confined CVD method improves the crystallinity of ultrathin GeTe by lowering the partial pressure of the reactant gas, resulting in GeTe nanosheets with excellent p-type semiconductor properties, such as a satisfactory on/off ratio of 10⁵. Temperature-dependent electrical measurements demonstrate that variable-range hopping and optical-phonon-assisted hopping mechanisms dominate transport behavior at low and high temperatures, respectively. GeTe devices exhibit significantly high responsivity (6589 and 2.2 A W⁻¹ at 633 and 980 nm, respectively) and detectivity (1.67 × 10¹¹ and 1.3 × 10⁸ Jones at 633 and 980 nm, respectively), making them feasible for broadband photodetectors in the visible to near-infrared range. Furthermore, the fabricated GeTe/WS₂ diode exhibits a rectification ratio of 10³ at zero gate voltage. These satisfactory p-type semiconductor properties demonstrate that ultrathin GeTe exhibits enormous potential for applications in optoelectronic interconnection circuits.

Atomically thin, p-type semiconducting SnSb₂Te₄ single crystals are grown via a chemical vapor deposition method. The SnSb₂Te₄-based photodetection devices show broadband detection through communication bands due to its bandgap of 0.42 eV and a fast response/recovery speed of tens of microseconds, exceeding most transition metal dichalcogenides, owing to its high room temperature mobility of 300 cm² V⁻¹s⁻¹.

Abstract

SnSb₂Te₄ (SST), a ternary van der Waals (vdW) material, has been widely investigated during last decades for potential applications in superconductivity, thermoelectricity, and optoelectronics. Recently, atomically thin SST has been predicted to show abnormal electronic band structure evolutions, high carrier mobility, and strong light–matter interaction. However, controllable synthesis of such SST crystals has been a huge challenge. Herein, atomically thin SST flakes are prepared via a chemical vapor deposition (CVD) method by using SbCl₃, SnCl₄·5H₂O, and Te as the precursors. Multiple structural characterizations reveal that the SST flakes are single crystals with high crystallinity. Due to the narrow bandgap of 0.42 eV, SST-based photodetectors have a broadband spectrum detection range from visible light through communication bands (480–1550 nm). More importantly, benefiting from a high room-temperature carrier mobility over 300 cm² V⁻¹ s⁻¹, the SST photodetectors demonstrate a response/recovery time of tens of tens of microseconds, which exceeds most typical transition metal dichalcogenide (TMDC) flakes. In addition, the photodetector maintains high performance after being exposed to the air for 2 months, suggesting good environmental stability. These excellent performances suggest that the SST flakes are promising for next-generation optoelectronics.

2D materials can be effectively produced by liquid phase exfoliation (LPE) using different conditions. LPE generates 2D materials in aqueous solutions, represented by graphene, black phosphorus, transition metal dichalcogenides and hexagonal boron nitride, and possess a huge potential in the biomedical domain, spanning cancer therapy, drug delivery as well as antimicrobial and biosensing.

Abstract

2D materials (2DMs), such as graphene, transition metal dichalcogenides (TMDs), and black phosphorus (BP), have been proposed for different types of bioapplications, owing to their unique physicochemical, electrical, optical, and mechanical properties. Liquid phase exfoliation (LPE), as one of the most effective up-scalable and size-controllable methods, is becoming the standard process to produce high quantities of various 2DM types as it can benefit from the use of green and biocompatible conditions. The resulting exfoliated layered materials have garnered significant attention because of their biocompatibility and their potential use in biomedicine as new multimodal therapeutics, antimicrobials, and biosensors. This review focuses on the production of LPE-assisted 2DMs in aqueous solutions with or without the aid of surfactants, bioactive, or non-natural molecules, providing insights into the possibilities of applications of such materials in the biological and biomedical fields.

In this article, an AI-robot-based autonomous platform developed for the bespoke design of metal nanoparticles with targeted optical properties is reported. This study highlights both capabilities of the platform to enhance search efficiencies and to provide novel chemical knowledge by analyzing datasets accumulated from the autonomous experimentation.

Abstract

The optimization of nanomaterial synthesis using numerous synthetic variables is considered to be an extremely laborious task because conventional combinatorial explorations are prohibitively expensive. In this work, an autonomous experimentation platform developed for the bespoke design of metal nanoparticles (NPs) with targeted optical properties is reported. This platform operates in a closed-loop manner between the batch synthesis module of metal NPs and the UV–vis spectroscopy module, based on the feedback of the AI optimization modeling. With silver (Ag) NPs as a representative example, it is demonstrated that the Bayesian optimizer implemented with the early stopping criterion can efficiently produce Ag NPs at room temperature precisely possessing the desired absorption spectra within only 200 iterations (when optimizing among five aqueous synthetic reagents). In addition to the outstanding material developmental efficiency, the analysis of synthetic variables further reveals a novel chemistry involving the quantitative effects of citrate in Ag NP synthesis. The amount of citrate is key to controlling the competition between spherical and plate-shaped NPs and, as a result, affects the shapes of the absorption spectra as well. This study highlights both capabilities of the platform to enhance search efficiencies and to provide novel chemical knowledge by analyzing datasets accumulated from autonomous experimentations.

The phonon polaritons formed by two infrared-active phonon modes in monolayer MoSi₂N₄ and WSi₂N₄ possess ultra-high confinement factors of around 10⁵ and 10³, and the Rabi splittings of the formed cavity-exciton polaritons reach 373 and 321 meV, respectively.

Abstract

The 2D semiconductors are an ideal platform for exploration of bosonic fluids composed of coupled photons and collective excitations of atoms or excitons, primarily due to large excitonic binding energies and strong light-matter interaction. Based on first-principles calculations, it is demonstrated that the phonon polaritons formed by two infrared-active phonon modes in monolayer MoSi₂N₄ and WSi₂N₄ possess ultra-high confinement factors of around ≈10⁵ and 10³, surpassing those of conventional polaritonic thin-film materials by two orders of magnitude. It is observed that the first bright exciton possesses a substantial binding energies of 750 and 740 meV in these two monolayers, with the radiative recombination lifetimes as long as 25 and 188 ns, and the Rabi splitting of the formed cavity-exciton polaritons reaching 373 and 321 meV, respectively. The effective masses of the cavity exciton polaritons are approximately 10⁻⁵ m _e , providing the potential for high-temperature quantum condensation. The ultra-confined and ultra-low-loss phonon polaritons, as well as strongly-coupled cavity exciton polaritons with ultra-small polaritonic effective masses in these two monolayers, offering the flexible control of light at the nanoscale, probably leading to practical applications in nanophotonics, meta-optics, and quantum materials.

Nature Communications, Published online: 08 March 2024; doi:10.1038/s41467-024-46293-w

Leveraging from thickness control methodology, vertical ferroelectric polarization switching is recorded on a 6 nm thick specimen probed by a piezoresponse force microscopy. The ferroelectric origin is uncovered by first-principles density-functional theory calculations. Bi₂O₂Se-based field-effect transistor demonstrated an unprecedented current on–off ratio of 10⁸ and carrier mobility of 131 cm² V⁻¹ s⁻¹. This work manifests the feasibility of 2D Bi₂O₂Se for next-generation electronics.

Abstract

The amelioration of atomically thin ferroelectric materials is imperative for next-generation outperformed two-dimensional (2D) electronics, which is elusive by their bulk counterparts. These remarkable materials’ ferroelectric and piezoelectric features are the fundamental urges in optoelectronics, electronics, and energy harvesting. In this work, 2D ferroelectric Bi₂O₂Se flakes have been synthesized using a modified chemical vapor deposition technique. The 6 nm thick Bi₂O₂Se flake provides a robust ferroelectric switching under an applied voltage of ±10 V by piezoresponse force microscopy, further confirmed by first principles. Leveraging the successful growth, the high-quality Bi₂O₂Se flakes permit the fabrication of a field-effect transistor (FET) with state-of-the-art performance. The FET device rewards a high current on–off ratio of 10⁸ and field effect mobility of almost 131 cm² V⁻¹ s⁻¹, owing to the small carrier effective mass of 0.2 m₀. Combined, the electric field-induced local polarization of ferroelectric switching and unprecedented device performance of Bi₂O₂Se semiconductors are certified for their utilization in advanced nanoelectronics and miniaturization of multifunctional devices with multifunctionalities.

The van der Waals (vdW) force has been regarded as a versatile and universal potential. Nevertheless, whether vdW force can be used as an attractive potential for the crystallization of colloids remains to be proven. Here, it is shown that the implementation of gold cores into silica colloids can reconfigure vdW force to optimal range in terms of colloidal crystallizations.

Abstract

A general guiding principle for colloidal crystallization is to tame the attractive enthalpy such that it slightly overwhelms the repulsive interaction. As-synthesized colloids are generally designed to retain a strong repulsive potential for the high stability of suspensions, encoding appropriate attractive potentials into colloids has been key to their crystallization. Despite the myriad of interparticle attractions for colloidal crystallization, the van der Waals (vdW) force remains unexplored. Here, it is shown that the implementation of gold cores into silica colloids and the resulting vdW force can reconfigure the pair potential well depth to the optimal range between −1 and −4 k_BT at tens of nanometer-scale colloidal distances. As such, colloidal crystals with a distinct liquid gap can be formed, which is evidenced by photonic bandgap-based diffractive colorization.

A negative-differential-resistance (NDR) device featuring a junctionless vdW channel. The approach for inducing the NDR phenomenon revolves around selectively inhibiting carrier transport, a result accomplished by creating a partial potential barrier within the junctionless channel. To showcase the utility of the junctionless NDR device for a ternary hardware neural network, its practical application is presented by configuring ternary logic circuits.

Abstract

Negative-differential-resistance (NDR) devices offer a promising pathway for developing future computing technologies characterized by exceptionally low energy consumption, especially multivalued logic computing. Nevertheless, conventional approaches aimed at attaining the NDR phenomenon involve intricate junction configurations and/or external doping processes in the channel region, impeding the progress of NDR devices to the circuit and system levels. Here, an NDR device is presented that incorporates a channel without junctions. The NDR phenomenon is achieved by introducing a metal-insulator-semiconductor capacitor to a portion of the channel area. This approach establishes partial potential barrier and well that effectively restrict the movement of hole and electron carriers within specific voltage ranges. Consequently, this facilitates the implementation of both a ternary inverter and a ternary static-random-access-memory, which are essential components in the development of multivalued logic computing technology.

Gravity-responsive soft actuators are created using liquid metal and thermoresponsive liquid crystal elastomer. The Joule heat of the liquid metal circuit with gravity-regulated resistance can be programmed by changing the actuator's pose to induce the flow of liquid metal. A gravity-adaptive actuator, a gravity-interactive gripper, and a self-regulated snapping oscillator or walker are also demonstrated.

Abstract

Plants can autonomously adjust their growth direction based on the gravitropic response to maximize energy acquisition, despite lacking nerves and muscles. Endowing soft robots with gravitropism may facilitate the development of self-regulating systems free of electronics, but remains elusive. Herein, acceleration-regulated soft actuators are described that can respond to the gravitational field by leveraging the unique fluidity of liquid metal in its self-limiting oxide skin. The soft actuator is obtained by magnetic printing of the fluidic liquid metal heater circuit on a thermoresponsive liquid crystal elastomer. The Joule heat of the liquid metal circuit with gravity-regulated resistance can be programmed by changing the actuator's pose to induce the flow of liquid metal. The actuator can autonomously adjust its bending degree by the dynamic interaction between its thermomechanical response and gravity. A gravity-interactive soft gripper is also created with controllable grasping and releasing by rotating the actuator. Moreover, it is demonstrated that self-regulated oscillation motion can be achieved by interfacing the actuator with a monostable tape spring, allowing the electronics-free control of a bionic walker. This work paves the avenue for the development of liquid metal-based reconfigurable electronics and electronics-free soft robots that can perceive gravity or acceleration.

Nature Synthesis, Published online: 07 March 2024; doi:10.1038/s44160-024-00501-z

npj 2D Materials and Applications, Published online: 06 March 2024; doi:10.1038/s41699-024-00456-x

Highly efficient room-temperature nonvolatile magnetic switching by current is realized in a single-material device based on vdW ferromagnet Fe₃GaTe₂. This result is mainly caused by the spin-orbit-torque effect in Fe₃GaTe₂ itself. Moreover, the switching current density and the power dissipation are several orders of magnitude smaller than those in conventional spin-orbit-torque devices of magnet/heavy-metal heterostructures.

Abstract

Effectively tuning magnetic state by using current is essential for novel spintronic devices. Magnetic van der Waals (vdW) materials have shown superior properties for the applications of magnetic information storage based on the efficient spin torque effect. However, for most of known vdW ferromagnets, the ferromagnetic transition temperatures lower than room temperature strongly impede their applications and the room-temperature vdW spintronic device with low energy consumption is still a long-sought goal. Here, the highly efficient room-temperature nonvolatile magnetic switching is realized by current in a single-material device based on vdW ferromagnet Fe₃GaTe₂. Moreover, the switching current density and power dissipation are about 300 and 60000 times smaller than conventional spin-orbit-torque devices of magnet/heavy-metal heterostructures. These findings make an important progress on the applications of magnetic vdW materials in the fields of spintronics and magnetic information storage.

Nature Materials, Published online: 04 March 2024; doi:10.1038/s41563-024-01839-7

Here, a time-dependent information encryption model from a liquid crystalline polymer with a programmable glass transition temperature (T _g) and gradually adjustable fluorescence is presented. The programmable T _g is achieved by adjusting the degree of order of the materials via a configuration interconversion of spiropyran-based materials (SPBMs), and the gradually adjustable fluorescence is achieved via a fluorescence resonance energy transfer effect.

Abstract

Time-dependent dynamic information encryption technology is a promising approach to enhancing the security and complexity of information transmission. Herein, a time-dependent information encryption model from a liquid crystalline polymer (LCP) film with a programmable glass transition temperature (T _g) and gradually adjustable fluorescence is demonstrated. The programmable T _g is achieved by adjusting the degree of order of the LC molecules via a configuration interconversion of spiropyran-based materials (SPBMs), which can convert between a V-shaped colorless spiro (SP) and a rodlike dark-colored merocyanine (MC) form. An LCP film obtained by visible light polymerization exhibits a lower T _g than UV light, because the SPBM molecules keep different configurations in the two films. By adjusting the ratio of two isomerization forms of SPBM molecules during the polymerization process, the T _g values of LCP films can change from 11.6 °C to 31.1 °C. Based on the isomerization rate of SPBM in the LCP films with different T _g, time-dependent information encryption is successfully achieved.

The use of nanowires with different diameters as the bending media to fabricate 2D α-In₂Se₃/β-InSe heterojunctions with large curvatures as high as 1 × 10⁶ m⁻¹ is proposed. This strategy allows us to demonstrate the first successful modulation of self-powered photodetection in 2D heterojunctions via a strong flexoelectric effect.

Abstract

The unique morphology of 2D van der Waals materials enables them to withstand large deformations and significant nonuniform strain, potentially inducing a strong flexoelectric effect. Despite the size-dependent flexoelectric effect showing potential for modulating the optoelectronic performance of 2D van der Waals materials, it is far from being fully exploited owing to various challenges. Herein, the use of nanowires with different diameters as the bending media to fabricate 2D α-In₂Se₃/β-InSe heterojunctions with large curvatures of 0.1–1 µm⁻¹ is proposed. The significant band alignment modulation in α-In₂Se₃ resulting from the bending-induced flexoelectric effect is verified through Kelvin probe force microscopy. The strain-induced piezoelectric effect can be negated because of the weak vdW forces at the interface. The flexoelectric polarization in β-InSe is screened via the accumulated electrons in the unilateral depleted heterojunction. Compared to the flat heterojunction, the curved heterojunction with an average curvature of 0.9 µm⁻¹ shows 2.48-fold and 7.62-fold increases in open-circuit voltage and zero-biased responsivity, respectively. This study demonstrates the first successful modulation of photodetection in 2D heterojunctions by exploiting the flexoelectric effect, providing a new perspective for high-performance 2D vdW optoelectronic devices.

Implanting atoms modifies the properties of materials aimed to targeted functionalities. Doping silicon and similar materials by implantation is crucial for developing efficient semiconductors. Ga implantation in hydrogenated WS₂ nanostructures produces efficient doping. High-dose Ga⁺ irradiation damages pristine structures, while low doses are ineffective. Hydrogenation by radiofrequency-activated plasma enables Ga implantation, offering potential for novel nanomaterials.

Abstract

Bombarding WS₂ multilayered nanoparticles and nanotubes with focused ion beams of Ga⁺ ions at high doses, larger than 10¹⁶ cm⁻², leads to drastic structural changes and melting of the material. At lower doses, when the damage is negligible or significantly smaller, the amount of implanted Ga is very small. A substantial increase in the amount of implanted Ga, and not appreciable structural damage, are observed in nanoparticles previously hydrogenated by a radio-frequency activated hydrogen plasma. Density functional calculations reveal that the implantation of Ga in the spaces between adjacent layers of pristine WS₂ nanoparticles is difficult due to the presence of activation barriers. In contrast, in hydrogenated WS₂, the hydrogen molecules are able to intercalate in between adjacent layers of the WS₂ nanoparticles, giving rise to the expansion of the interlayer distances, that in practice leads to the vanishing of the activation barrier for Ga implantation. This facilitates the implantation of Ga atoms in the irradiation experiments.